An earth pressure shield can have a front working compartment having at least one digging or mining tool and formed by a separating wall, in which a circular space is formed with a top region connected with a regulated pressurized air feed and with a bottom region open to the digging or mining tool so that the dug or mined earth material is removable with the help of a conveyor unit. At least one fluid pipe is guided from a fluid chamber with a first level controller and a fluid feeder to a fluid outlet open to the digging or mining tool.
The separating wall forms a reinforcing annular space which is triangular in cross section in which earth material mixed with fluid can enter whereby the corresponding fluid pipe or duct can be clogged.
Tunnels are driven through loose earth with a tunnel and/or gallery digging machine. For support of the local front wall during digging or mining of the earth the partitioned or compartmentalized front part of the tunnel and/or gallery digging machine advantageously is filled with a fluid which stands under a regulated pressure.
In this partitioned portion the digging unit itself is located, usually a digging wheel with which the earth is loosened. This loosened earth then drops into the supporting fluid and is pumped together with it from the partitioned region and fed to a separating plant. There the earth is separated from the supporting fluid and the fresh supporting fluid is pumped into the front partitioned portion of the tunnel and/or gallery digging machine.
This process has proven to be effective, particularly when in the partitioned portion of the tunnel and/gallery digging machine, the so-called working compartment, an immersed wall is formed and extends almost to the base of the unit and in the rear part of the machine, which is separated from the working compartment by the immersed wall, a regulatable pressurized air cushion or reservoir provides a constant pressure to the supporting fluid at the local front wall.
Because of the pressure cushion pressure fluctuations are reduced, which would arise if the volume of the pumped supporting fluid enriched with earth material was not enough to correspond or keep up with the purified fluid fed back to the machine.
Other methods are known in which the fluid flow rates from and to the unit are measured in operation. Volume differences arising can then be balanced by regulating valves and pumps. However these mechanical devices react slowly in comparison to the automatic pressure balancing due to the pressurized air cushion and in fact the pressure fluctuations in the supporting fluid are thus larger.
The above described method is however limited to earth in which the solid earth components can be separated in a separating unit from the supporting fluid. This is not possible in coherent earth with a high solid component or only at great cost. Tunnels in this earth are driven with tunnel and/or gallery digging machines with which the loosened earth material instead of the supporting fluid should support the local front wall in the partitioned working compartment.
This earth material is however substantially more viscous and is pumped from the working compartment not with a rotary pump, but is usually with a conveyor unit. It is predominantly removed and deposited without additional processing. The reliable support of the local front wall is however problematical.
In the tunnel and/or gallery machine known up to now, an attempt is made to provide a constant supporting pressure on the local front wall and to guarantee because of that that volume of earth material dug by the digging wheel is never less than that removed by the conveyor. This is effected by control and regulation of the tunneling pressure of the tunnel and gallery digging machine and the performance of the conveyor. However the control and regulating elements for doing this are too coarse.
When too much earth is removed from the working compartment, the supporting pressure is lowered. The local front wall is released from the applied pressure. Earth from above the roof of the tunnel and/or gallery digging machine is forced into the tunnel cross section and the surface of the ground above is lowered.
If too little earth is removed or withdrawn from the working compartment, the earth material obtained is compressed. It is thus inclined to clog the conveyor unit. An increased supporting pressure on the local front wall occurs acting to lift the surface of the ground.
To minimize these undesirable possibilities, pressure cells are built in at the rear wall of the working compartment to maintain a reliable direct measurement of the supporting pressure in the working compartment.
However the pressure measuring devices are usually unreliable instruments. They are often driven off scale by the relatively rigid earth material. Moreover they only give information about the pressure in a very limited local region.
An essential basis for reliable support of the local front wall in a tunnel and/or gallery digging machine which itself uses the dug earth material as a supporting medium which is only as reliable as necessary is the following: the earth material is compressible and thus pressure can be transmitted only in a locally limited way. That has the consequence that the attained supporting pressure on the local front wall, especially in the vicinity of the roof of the tunnel and/or galler digging machine, can not be reliably transmitted. An increase of the generated earth material considerably changes the transmittability of a supporting pressure.
In the processes known up to now the attempt is made to overcome the above mentioned disadvantages by feeding in water or a suspension locally or, more generally, ground material which has physical properties approaching those of a viscous fluid into the working compartment. Furthermore mixing vane elements on the digging wheel and on the pressure wall are built in to mix the earth material with the fed in fluid and provide a homogeneous mixture.
Methods are known with which a fluid is pumped in the space directly in front of the digging wheel through the arms of the digging wheel when the digging wheel loosens the earth.
Also processes exist in which by regulated injection of fluid, e.g. in the region of the roof, an attempt is made to attain at least a constant supporting pressure there.
However in all these endeavors mechanical devices are used which only react slowly such as valves and pumps. Also the measuring devices used only can contribute to a certain extent to an increase in the reliability of the supporting pressure on the local front wall.